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Plastic as a vapor barrier attic insulation

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Plastic as a vapor barrier attic insulation Colbyt 07-26-2008
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Posted by Colbyt on July 26, 2008, 6:46 pm


I am about to install some batt insulation in an old ceiling where the joist
placement must have been determined by the number of remaining boards on the
job site. Meaning absolutely nothing is 16" CC.

I am going to use unfaced batts as they are much easier to trim to fit.
Then I am thinking of using 4 mil plastic off the roll stapled to the
joists for the vapor barrier. This is quite common in wall areas but I have
never done or seen it in a ceiling application.

Comments. Suggestions.

Colbyt



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Posted by on July 26, 2008, 7:59 pm


> I am about to install some batt insulation in an old ceiling where the jo=
ist
> placement must have been determined by the number of remaining boards on =
the
> job site. Meaning absolutely nothing is 16" CC.
>
> I am going to use unfaced batts as they are much easier to trim to fit.
> Then I am thinking of using =A04 mil plastic off the roll stapled to the
> joists for the vapor barrier. =A0This is quite common in wall areas but I=
have
> never done or seen it in a ceiling application.
>
> Comments. Suggestions.
>
> Colbyt

No problem, in fact I have seen it done a lot around here.

Posted by on July 27, 2008, 7:30 am


On Jul 26, 7:59=A0pm, jmee...@columbus.rr.com wrote:
>
> > I am about to install some batt insulation in an old ceiling where the =
joist
> > placement must have been determined by the number of remaining boards o=
n the
> > job site. Meaning absolutely nothing is 16" CC.
>
> > I am going to use unfaced batts as they are much easier to trim to fit.
> > Then I am thinking of using =A04 mil plastic off the roll stapled to th=
e
> > joists for the vapor barrier. =A0This is quite common in wall areas but=
I have
> > never done or seen it in a ceiling application.
>
> > Comments. Suggestions.
>
> > Colbyt
>
> =A0 No problem, in fact I have seen it done a lot around here.

Actually, I do see a problem. Not sure exactly how this is proposed
to be installed, but from the wording, it sounds like the insulation
could be going in first, followed by the vapor barrier over top? If
so, that is incorrect. The vapor barrier should be against the
ceiling, the insulation on top.

Posted by Colbyt on July 27, 2008, 4:52 pm



On Jul 26, 7:59 pm, jmee...@columbus.rr.com wrote:
>
> > I am about to install some batt insulation in an old ceiling where the
> > joist
> > placement must have been determined by the number of remaining boards on
> > the
> > job site. Meaning absolutely nothing is 16" CC.
>
> > I am going to use unfaced batts as they are much easier to trim to fit.
> > Then I am thinking of using 4 mil plastic off the roll stapled to the
> > joists for the vapor barrier. This is quite common in wall areas but I
> > have
> > never done or seen it in a ceiling application.
>
> > Comments. Suggestions.
>
> > Colbyt
>
> No problem, in fact I have seen it done a lot around here.

Actually, I do see a problem. Not sure exactly how this is proposed
to be installed, but from the wording, it sounds like the insulation
could be going in first, followed by the vapor barrier over top? If
so, that is incorrect. The vapor barrier should be against the
ceiling, the insulation on top.

NO. Insulation in first held in place wire light wire stapled to the bottom
of the joists and then plastic stapled to the room side and covered with
drywall.

Spray in foam may be a good option for some installations but not his one.
For all practical purposes this is the same as a cathedral ceiling. Just
enough room above for a little air flow.

Colbyt



Posted by hallerb@aol.com on July 27, 2008, 8:10 am


:
> I am about to install some batt insulation in an old ceiling where the jo=
ist
> placement must have been determined by the number of remaining boards on =
the
> job site. Meaning absolutely nothing is 16" CC.
>
> I am going to use unfaced batts as they are much easier to trim to fit.
> Then I am thinking of using =EF=BF=BD4 mil plastic off the roll stapled t=
o the
> joists for the vapor barrier. =EF=BF=BDThis is quite common in wall areas=
but I have
> never done or seen it in a ceiling application.
>
> Comments. Suggestions.
>
> Colbyt

Vapor barrier goes to the warm side...... inside in cold climates,
outward in warm climates.

expanding closed cell spray foam costs more but at R6 or R7 per inch
is a far superior insulation to fiberglass, seals all the little
cracks etc, which saves energy and stops noise too, noise is
transfered thru air passages, which dont exist with spary foam.

plus it requires no vapor barrier. its naturally one.

can get local contractor to install, joist width and obstructions
meaningless..

I was told theres drums available for DIY jobs.

its a realtive of the small cans of sealing foam like great stuff.

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